Regioregular Head-to-Tail Poly(4-alkylquinoline)s: Synthesis, Characterization, Self-Organization, Photophysics, and Electroluminescence of New n-Type Conjugated Polymers

Article abstract of DOI:10.1021/ma0348021

Five poly(4-alkylquinoline-2,6-diyl)s (P4AQs), having 100% head-to-tail regioregularity, were synthesized, characterized, and explored as emissive and electron transport materials in polymer light-emitting diodes. The organic solvent (chloroform, tetrahyd

Full text of DOI:10.1021/ma0348021

8958
Macromolecules 2003, 36, 8958-8968
Regioregular Head-to-Tail Poly(4-alkylquinoline)s: Synthesis,
Characterization, Self-Organization, Photophysics, and
Electroluminescence of New n-Type Conjugated Polymers
Ya n Zh u , Ma k su d u l M. Ala m , a n d Sa m son A. J en ek h e*
Department of Chemical Engineering and Department of Chemistry, University of Washington,
Seattle, Washington 98195-1750
Received J une 13, 2003; Revised Manuscript Received September 28, 2003
ABSTRACT: Five poly(4-alkylquinoline-2,6-diyl)s (P4AQs), having 100% head-to-tail regioregularity, were
synthesized, characterized, and explored as emissive and electron transport materials in polymer light-
emitting diodes. The organic solvent (chloroform, tetrahydrofuran, methylene chloride, etc.) soluble poly-
(4-alkylquinoline)s had reversible electrochemical reduction with an electron affinity (2.6 eV) that was
independent of alkyl chain length. X-ray diffraction studies showed that solution-cast films of regioregular
P4AQs have self-organized lamellar structures with an interchain π-stacking distance of 3.9-4.1 Å and
an interlayer d-spacing that varied linearly from 13.4 Å for butyl to 22.3 Å for tridecyl side chains. The
new poly(4-alkylquinoline)s emit blue light at 423-426 nm in dilute chloroform solution and yellow light
at 542-557 nm in the solid state. Yellow electroluminescence with a luminance of up to 86 cd/m2 and an
external quantum efficiency of up to 0.6% was observed for the P4AQs as emissive materials. A large
improvement in performance of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene)-based light-
emitting diodes (a luminance of up to 700 cd/m2 and an external quantum efficiency of up to 3.0%) was
observed when the P4AQs were used as the electron transport materials. The new regioregular poly(4-
alkylquinoline)s are promising n-type conjugated polymer semiconductors for electronic and optoelectronic
devices.
In tr od u ction
layered crystalline films, exhibit superior properties,
such as better ordering and crystallinity,14 higher
charge carrier mobility,4 and enhancement in electrical
conductivity when compared to regiorandom analogues.
They have found device applications in field-effect
transistors4 and photovoltaic cells6b due to their high
hole mobility resulting from the well-organized lamellar
structure in films. Although it can be expected that
regioregular n-type π-conjugated polymers will similarly
have improved self-ordering and thus higher electron
Conjugated polymer semiconductors are of growing
interest as active elements in electronic and photonic
devices including light-emitting diodes,1-3 thin film
transistors,4,5 photovoltaic cells,6,7 and electrochromic
cells.8 Most of the conjugated polymers that have been
widely investigated and explored in these device ap-
plications are p-type (electron donor, hole transport)
materials exemplified by the polythiophenes, poly-
(phenylenevinylene)s, polyfluorenes, and polyphenyl-
enes.1-9 n-Type (electron acceptor, electron transport)
conjugated polymer semiconductors are also needed for
developing improved light-emitting diodes (LEDs), thin
film transistors, photovoltaic cells, and other elements
of plastic electronics. In the case of field-effect transis-
tors, high electron mobility conjugated polymers are
needed for developing n-channel devices essential for
designing and producing plastic integrated circuits.4,5
Such n-type conjugated polymers having high electron
mobility are also essential to achieving high-efficiency
solar cells based on bipolar polymer blend or the layered
heterojunction architecture.6,7 Although a few classes
of n-type conjugated polymers, such as the polyquino-
lines,10 polyquinoxalines,11 polypyridine,12 and poly-
benzobisazoles,3h,13 have been explored as electron
transport materials in polymer LEDs, the current
materials either lack solubility in common organic
solvents or are regiorandom and thus lack the ability
to self-organize into ordered crystalline thin films.
Regioregular alkylated π-conjugated polymers, exem-
plified by the regioregular poly(3-alkylthiophene)s, have
attracted much recent attention because of their ability
to self-organize into highly ordered crystalline films that
have shown distinctive electronic and optical proper-
ties.14 It has been shown that regioregular, head-to-tail,
poly(3-alkylthiophene)s (P3ATs), which self-order into
mobility, few such polymers are currently known.5,12
A
regioregular, head-to-tail, poly(6-hexylpyridine-2,5-diyl)
that self-orders into layered crystalline films has been
prepared by Yamamoto12 but is yet to be fully explored
as an n-type semiconductor in devices. We have thus
been interested in the regiocontrolled synthesis and
investigation of new regioregular n-type π-conjugated
polymers for electronic device applications.
Many phenylated polyquinolines have been synthe-
sized and extensively investigated due to their high
thermal and oxidative stability, outstanding mechanical
properties, and optical and electronic properties.10,15,16
On the basis of their excellent electron-accepting prop-
erties,15 the phenylated polyquinolines have been ex-
tensively explored as emissive and electron transport
materials in light-emitting devices.3c-h,9 The effects of
molecular and supramolecular structures on the elec-
troluminescence and photophysical properties of a series
of polyquinolines were also extensively studied.3f How-
ever, nearly all of the currently known phenylated
polyquinolines are not soluble in aprotic organic solvents
unless via complexation,10,15,17 thus limiting their use
in polymer devices of various architectures.3,9 They also
lack capacity for self-organization into ordered struc-
tures driven by alkyl side chains.
10.1021/ma0348021 CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/30/2003

Macromolecules, Vol. 36, No. 24, 2003
Poly(4-alkylquinoline)s 8959
Sch em e 1
Ta ble 1. Molecu la r Weigh ts a n d Th er m a l P r op er ties of
P oly(4-a lk ylqu in olin e)s
In this paper, we report the regiocontrolled synthesis,
self-organization, and properties of a series of organic
solvent soluble, 100% regioregular, head-to-tail, poly-
(4-alkylquinoline)s with various alkyl side chains. Elec-
trochemical redox experiments showed that the new
polymers had reversible reduction and photophysical
properties that were independent of the alkyl chain
length. We find that these polymers can self-organize
into layered highly ordered structures in solution-cast
solid films. A linear correlation between the interlayer
d-spacing and the number of carbon atoms in the alkyl
side chain was found, confirming that the rigid-rod main
chains are spaced by the alkyl side chains. We explored
use of the new n-type conjugated polymers in light-
emitting diodes (LEDs) as both the emissive and elec-
tron transport materials. A large improvement in
performance of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-
phenylenevinylene) (MEH-PPV)-based LEDs was ob-
served when the poly(4-alkylquinoline)s were used as
the electron transport materials. In a preliminary
communication, we reported the synthesis and initial
study of two members of the poly(4-alkylquinoline)s, i.e.,
poly(4-hexylquinoline) and poly(4-octylquinoline).18
residual
a
a
b
polymer yield (%)
Mw
Mw/Mn
Td (°C) weightc (%)
P4BQ
P4HQ
P4OQ
P4DQ
P4TDQ
85
91
87
90
90
d
d
447
460
460
440
437
67
63
57
54
36
15 150
10 250
23 100
9 200
2.79
4.02
3.50
2.48
a
Molecular weights were determined by GPC in chloroform
b
based on polystyrene standards. Onset decomposition tempera-
ture measured by TGA under N2. c Residual weights determined
d
by TGA under N2 up to 900 °C. No molecular weight was
determined due to the incomplete solubility of P4BQ in organic
solvents.
the yield of this step is low (25-30%), the reaction is
very clean, allowing the starting materials to be readily
recovered and reused. The polymers were synthesized
by acid-catalyzed Friedla¨nder condensation polymeri-
zation with good yields in a range of 85-91%, as shown
in Table 1. The molecular structures of poly(4-alkyl-
quinoline)s were confirmed by 1H NMR, FT-IR, and
1
UV-vis spectra. A representative H NMR spectrum of
P4HQ in trifluoroacetic acid-d (CF3COOD) is shown in
Figure 1 (see Supporting Information for other P4AQs).
We used CF3COOD as the NMR solvent because of the
Resu lts a n d Discu ssion
1
Syn th esis a n d Ch a r a cter iza tion . The synthesis of
the monomers (4a -4e) and their self-polymerization to
the corresponding 100% regioregular poly(4-alkylquino-
line)s (5a -5e) are outlined in Scheme 1. The new AB-
type monomers 4a -4e were prepared in four steps by
modifying a reported method.19 We ran the third step
reaction at 80 °C instead of the reported 60 °C,19 and
we doubled the reaction time. The yield of the first step
was moderate, 45-62%. The 87-95% yield of the second
step was very good and is much higher than the
literature value.19 The third step involves controlled
oxidation of an ethyl group to an acetyl group. Although
overlap of the H NMR chemical shifts of other deuter-
ated solvents such as chloroform-d with those of protons
in P4AQs. The 1H NMR spectra were in good agreement
with the structures of the polymers. The overall inte-
gration ratios between the aliphatic protons and the
aromatic protons were consistent with the structures
of the polymers. The 100% head-to-tail regioregularity
of the P4AQs automatically follows from the AB-type
condensation polymerization. In addition, the presence
of a nonsplitting peak at 3.74-3.78 ppm, which corre-
sponds to the R-methylene protons of the alkyl groups
in head-to-tail linkage, further confirmed the regioregu-

8960 Zhu et al.
Macromolecules, Vol. 36, No. 24, 2003
F igu r e 1. 1H NMR spectrum of P4HQ in trifluoroacetic acid-
d. Solvent and impurity peaks at 4.0, 6.9, 8.3, and 11.5 ppm.
F igu r e 2. FT-IR spectra of P4HQ and P4HQ monomer.
lar structures of the P4AQs.14c The singlet peak at 3.05-
F igu r e 3. (A) X-ray diffraction patterns of solution-cast films
of poly(4-alkylquinoline)s. (B) Interlayer d-spacing vs the
number of carbons in the alkyl chains.
1
3.11 ppm in the H NMR spectra of these polymers can
be assigned to the terminal acetyl protons in the
polymer chains.
of P4AQs except P4BQ are summarized in Table 1. We
did not do gel permeation chromatography (GPC) of
P4BQ because of its incomplete solubility in organic
solvents. The remaining P4AQs have moderate weight-
average molecular weights of 9200-23 100 with poly-
dispersity indices (Mw/Mn) of 2.48-4.02 based on poly-
styrene standards. The absolute number-average mol-
ecular weights of P4AQs can also be determined from
end-group analysis by 1H NMR spectroscopy. The
number-average molecular weights of the polymers so
determined were 3477 (P4BQ), 4853 (P4HQ), 4302
(P4OQ), 5340 (P4DQ), and 4944 (P4TDQ). As shown in
Table 1, all the P4AQs possess excellent thermal stabil-
ity with onset decomposition temperature (Td) ranging
from 437 to 460 °C in nitrogen as revealed in thermo-
gravimetric analysis (TGA). The 5% weight loss tem-
peratures of P4AQs in nitrogen were also in the range
424-464 °C. High residual weights of 36-67% were
observed for the series of P4AQs even at 900 °C under
N2. The residual weights of P4AQs decreased with the
length of the alkyl side chain. No clear phase transitions
were observed in differential scanning calorimetry
(DSC) scans of these polymers up to 300 °C.
The molecular structures of P4AQs were also con-
firmed by FT-IR spectra. Representative FT-IR spectra
of P4HQ and P4HQ monomer are shown in Figure 2.
The strong peaks at 1656-1671 cm-1 owing to the
carbonyl groups in 4a -4e have almost completely
disappeared in the poly(4-alkylquinoline)s. In addition,
the two peaks at 3300-3450 cm-1 in the monomers
corresponding to primary amines were absent in the FT-
IR spectra of the polymers. Instead, new strong bands
between 1600 and 1400 cm-1 due to the imine (CdN)
group and characteristic of the quinoline ring were
observed.10a-c These results confirm the completeness
of quinoline ring-forming cyclization. The presence of
alkyl side chains in the monomers lowered the reactivity
compared to the phenyl-substituted monomers.10a-c
A
higher reaction temperature (180 °C) and longer po-
lymerization time was required to get the complete
cyclization in poly(4-alkylquinoline)s compared to the
140 °C normally used in the synthesis of phenylated
polyquinolines.10a-c
The poly(4-alkylquinoline)s except for P4BQ are
soluble in common organic solvents, such as chloroform,
THF, and methylene chloride. P4BQ is only partially
soluble in chloroform or THF due to its short side chain.
As expected, the solubility of P4AQs in common organic
solvents increased with the length of the alkyl side
chain. The P4AQs are also soluble in protonic acid
solvents such as formic acid that are commonly used
for phenylated polyquinolines.10a-c The molecular weights
Self-Or ga n ized Str u ctu r es in F ilm s. Wide-angle
X-ray diffraction (WAXD) patterns of films of P4AQs
cast from chloroform or formic acid solutions are shown
in Figure 3A. The WAXD patterns showed a strong first-
order reflection at a 2θ angle of 6.61°, 5.63°, 5.0°, 4.49°,
and 3.96° for P4BQ, P4HQ, P4OQ, P4DQ, and P4TDQ,
respectively. This first-order reflection can be assigned

Macromolecules, Vol. 36, No. 24, 2003
Poly(4-alkylquinoline)s 8961
shown that the packing of the alkyl chains in head-to-
tail regioregular poly(3-alkylthiophene)s adopts an end-
to-end model with a tilting angle of 50°, giving a slope
of 1.8 Å per carbon atom for a similar d-spacing vs alkyl
chain carbon number plot.21b In our case, we concluded
that the alkyl chains in head-to-tail regioregular P4AQs
interdigitate in view of the observed slope of 0.99 Å per
carbon atom and the smaller grafting density of the
alkyl chains on the polymer main chain compared to
that of poly(3-alkylthiophene)s. The tilting angle of the
interdigitated alkyl chains of P4AQs was estimated to
be 52° based on the slope (0.99 Å/carbon atom) and the
effective length of CH2-CH2 group (1.25 Å).
The interdigitation mode of alkyl chain packing in the
P4AQs can also be concluded from the results of Figure
3B by the following analysis. An effective distance
between the two main chains without any alkyl side
chain is estimated to be 9.65 Å from the intercept of
the plot in Figure 3B. Therefore, a d-spacing of about
17.15 Å (9.65 + 1.25 × 6 Å) should be observed in P4HQ
if the hexyl side chains adopt an interdigitation packing
mode. Since a d-spacing of 15.7 Å was actually found
for P4HQ, the packing of the hexyl chains in P4HQ must
be interdigitated with a certain tilt angle. A tilt angle
of 52° of the hexyl group in P4HQ was obtained from
the experimental d-spacing (15.7 Å) and the calculated
d-spacing (17.15 Å). Similar conclusions were reached
for the other P4AQs.
F igu r e 4. Schematic of layered and π-stacking structures of
regioregular poly(4-alkylquinoline)s exemplified for poly(4-
hexylquinoline).
to the (100) reflection, corresponding to an interlayer
d-spacing of 13.4, 15.7, 17.7, 19.7, and 22.3 Å for P4BQ,
P4HQ, P4OQ, P4DQ, and P4TDQ, respectively. Com-
pared to the regioregular poly(3-alkylthiophene)s,14c the
interlayer d-spacing is a little shorter in the poly(4-
alkylquinoline) with the same alkyl side chain. In
contrast to the relatively intense WAXD reflections from
solution-cast films of P4AQs, very weak and broad first-
order diffractions were observed in the powdered samples
of P4AQs. The main reason for this observation is that
the macromolecules of P4AQs can self-organize into
ordered layered structures more easily on a substrate
when the solvent slowly evaporates from the solution-
cast films than in the powdered samples. Since the (100)
reflections of P4AQs are observed in the out-of-plane
scan of X-ray diffraction, we suggest that the highly
ordered layered structures in the films of P4AQs are
preferentially oriented normal to the substrate. The
average crystallite size (L) of P4AQs normal to the (100)
planes can be estimated from the width of the (100)
reflection peaks by using the Scherrer equation (L )
λ/(â0 cos θ), where λ is wavelength, θ is the Bragg
reflection angle, and â0 is the full width at half-
maxima).20 The estimated mean crystallite size of the
P4AQs was 6.1, 7.1, 7.3, 8.4, and 11.2 nm for P4BQ,
P4HQ, P4OQ, P4DQ, and P4TDQ, respectively. It
appears that a longer alkyl side chain in the P4AQs
enhances the interlayer structural order with improve-
ment in the crystallite size. The broad peaks in the
diffraction patterns of P4AQs centered at 20.3°-22.4°
can be assigned to the (010) reflections, corresponding
to a spacing of 3.9-4.1 Å. This side-chain length
independent spacing is assigned to the π-stacking
distance in the P4AQs. The π-stacking distance in the
regioregular poly(4-alkylquinoline)s is thus larger than
the 3.6-3.8 Å observed in the regioregular poly(3-
alkylthiophene)s.14
As shown in Figure 3B, a plot of the interlayer
d-spacing vs the number of carbon atoms in the alkyl
side chain of the P4AQs gives a straight line with a slope
of 0.99 Å per carbon atom. The linear correlation clearly
indicates that the interlayer d-spacing corresponds to
a distance between the π-conjugated polymer main
chains separated by the alkyl side chains. It is known
that there are two common packing modes of alkyl chain
substituted polymers, interdigitation and end-to-end
packing.21 Because the CH2-CH2 group of the planar
zigzag conformation of an alkyl chain has an effective
distance of 1.25 Å along the alkyl chain axis, we expect
the d-spacing/carbon atom (slope) to be less than 1.25
Å in the interdigitation model (Figure 4) and between
1.25 and 2.5 Å in the end-to-end model if the tilting of
alkyl chain is taken into account. Previous work has
In summary, the X-ray diffraction results clearly show
that the new head-to-tail regioregular P4AQs self-
organize into layered order structures in which layers
of the rigid-rod main chains are spaced by interdigitated
and tilted alkyl side chains and have an interchain
π-stacking distance of 3.9-4.1 Å within each layer
(Figure 4). The alkyl side chains have a tilting angle of
52° in the solution-cast films of poly(4-alkylquinoline)s.
Since such self-organized ordered structures are known
to facilitate enhanced charge carrier mobility in poly-
(3-alkylthiophene)s,14 we expect the self-organized crys-
talline thin films of n-type P4AQs to offer good prospects
for electron transport in polymer devices. A novel self-
organization of the regioregular poly(4-alkylquinoline)s
in dilute solutions in protonic acid media was recently
discovered and is reported elsewhere.22 Future studies
will aim to understand whether any connection exists
between the ordered assemblies in solution and the
layered films in the solid state.
P h otop h ysica l P r op er ties. The optical absorption
and photoluminescence (PL) emission spectra of the
P4AQs in dilute chloroform solution and in the solid
state were obtained. Figure 5 shows the absorption and
PL emission spectra of the P4AQs in dilute chloroform
solution. All the P4AQs have strong featureless absorp-
tion bands and an identical lowest energy π-π* transi-
tion with a λmax at 385-387 nm (3.2 eV) in dilute
solution. Unstructured lowest energy absorption bands
are commonly observed in many π-conjugated polymers
due to the distribution of conjugation lengths, and thus
transition energies, that leads to a broadened absorption
and obscured vibronic structure. In addition to the
lowest energy π-π* transition band, there is an ad-
ditional higher energy absorption band at 274-276 nm
in each solution absorption spectrum of the P4AQ. The
solution PL emission spectra of all the P4AQs have well-
resolved vibronic structures (Figure 5B) and can thus
be assigned to the single-chain or “monomer” emission
states of the poly(4-alkylquinoline)s. The P4AQs emit

8962 Zhu et al.
Macromolecules, Vol. 36, No. 24, 2003
Ta ble 2. P h otop h ysica l a n d Red ox P r op er ties of P oly(4-a lk ylqu in olin e)s
a
absorption λmax (nm)
emission λmaxc (nm)
onset
red
Eogpt (eV)
solution
film
φf (solution)
φf (film)
E
(V)
Er°e′d e (V)
EA (eV)
b
d
polymer
solution
film
P4BQ
P4HQ
P4OQ
P4DQ
P4TDQ
PPQf
385
386
386
386
387
400
397
397
397
401
414
2.72
2.70
2.70
2.71
2.70
2.65
423
423
425
426
424
557
547
547
542
551
578
0.22
0.40
0.22
0.16
0.21
0.02
0.05
0.03
0.02
0.04
-1.77
-1.83
-1.81
-1.77
-1.82
-1.78
-1.87
-1.95
-1.95
-1.87
-1.92
-1.89
2.63
2.57
2.59
2.63
2.58
2.62
Absorption maxima in solution (chloroform, 10-6 mol/L) and as a thin film on silica substrate. Optical absorption edge gap (Egopt).
a
b
c Emission maxima in solution (chloroform, 10-6 mol/L) and as a thin film on silica substrate obtained by exciting at absorption λmax
.
Onset reduction potentials vs SCE. e Formal reduction potentials. f All the data for PPQ are from refs 3f and 15b.
d
F igu r e 5. Optical absorption spectra (A) and PL emission
F igu r e 6. Optical absorption (A) and PL emission (B) spectra
of P4AQs, 5a -5e, as thin films on silica substrates.
spectra (B) of P4AQs, 5a -5e, in chloroform solution (∼10-6 M).
blue light with an emission peak at 423-426 nm
corresponding to the 0-0 transition in dilute solution.
The 0-1 and 0-2 transitions in the PL emission spectra
were 454 and 485 nm, respectively. The main photo-
physical properties of the P4AQs in solution are col-
lected in Table 2.
The absorption spectra of P4AQ thin films are shown
in Figure 6A. These absorption spectra of P4AQs in the
solid state are very similar to those in solution. The
lowest energy π-π* transitions are centered at 397-
401 nm (∼3.1 eV) while an additional higher energy
band is found at 275-279 nm (∼4.5 eV) in each
spectrum. There is a 12-14 nm red shift in the lowest
energy absorption maximum compared to the corre-
sponding spectrum in dilute solution. This is due to an
increase in the planarity of the polymer chains and thus
an increase in conjugation length in the solid-state
resulting from the efficient π-stacking. The solid-state
π-π* transitions of the P4AQs are slightly blue shifted
compared to the phenylated poly(4-phenylquinoline)3f
(PPQ, λmax ) 414 nm), indicating a small decrease of
electron delocalization along the conjugated backbone
as the side group changes from phenyl to alkyl. The
absorption spectra of P4AQs with different alkyl chains
have identical absorption maxima and spectral shape
in dilute solution and in the solid state, showing that
the alkyl chain length did not have an effect on the
ground-state electronic structures of the P4AQs. The
optical band gaps (Egopt) determined from the absorption
edge of the solid-state spectra of the P4AQs are all
essentially identical at 2.7 eV, which is a little larger
than that of the phenylated derivative PPQ (2.65 eV).
Figure 6B shows the PL emission spectra of P4AQ
thin films. They emit yellow light in thin films with PL
emission peaks at 542-557 nm. This represents a 20-
30 nm blue shift compared to the orange PL emission

Macromolecules, Vol. 36, No. 24, 2003
Poly(4-alkylquinoline)s 8963
similar, being in the range of -1.95 to -1.87 V vs SCE
(Table 2).24 We estimated the electron affinity (EA,
LUMO level) of the P4AQs to be virtually identical,
2.57-2.63 eV,24 from the onset reduction potentials by
taking the SCE energy level to be -4.4 eV below the
onset
red
vacuum level (EA ) E
+ 4.4). If the SCE energy
level is instead -4.8 eV, the estimated EA values
increase to 3.0 eV. The onset potential, formal potential,
and the electron affinity of the P4AQs show little or no
change with the alkyl chain length. These redox proper-
ties were only slightly changed compared to those of
poly(4-phenylquinoline).15b These results suggest that
the electrochemical properties of this class of conjugated
polymers are determined primarily by the polyquinoline
backbone structure. The observed reversible reduction
and high electron affinity suggest that the poly(4-
alkylquinoline)s are intrinsic n-type (electron transport)
conjugated polymers similar to the phenylated poly-
quinolines.3f,15b
However, unlike the phenylated polyquinolines,15b the
present alkylated polyquinolines did not have a clear
oxidation wave as shown in Figure 7B. A rough estimate
of the ionization potential (IP, HOMO level) for the
onset
ox
P4AQs (IP ) E
+ 4.4) from the oxidation cyclic
voltammograms is ca. 5.4 eV or greater. Alternatively,
the HOMO levels of P4AQs can be obtained from their
electron affinities and optical band gaps (IP ) EA +
Eogpt) to be in the range 5.27-5.35 eV. The reversible
reduction and absence of clear oxidation suggest that
the P4AQs are excellent candidates for n-type doping
(electron transport) and hole blocking in devices.
Ligh t-Em ittin g Diod e P r op er ties. Light-emitting
diodes (LEDs) based on P4AQs both as emissive and as
electron transport materials were fabricated and inves-
tigated. We found that the intrinsic electroluminescence
(EL) of the poly(4-alkylquinoline)s in single-layer ITO/
PEDOT/5b-5e/Al type devices was very weak with a
luminance of 4-21 cd/m2. Yellow electroluminescence
with an emission peak at 550-552 nm was observed in
four of the P4AQs, 5b-5e. P4BQ (5a ) did not show EL
emission in a single-layer device. The EL spectra of
P4HQ, P4OQ, and P4TDQ are shown in Figure 8A. The
EL emission spectra are nearly identical to PL emission
spectra, and this means that the P4AQs function as
emissive materials in these diodes. This also means that
the EL emission is from intermolecular excimers as
shown for the PL spectra. The turn-on voltage of the
devices was high at 12.5-15 V. The corresponding
external quantum efficiency (EQE) was very low, 0.003-
0.008% (Table 3).
The difference between the IP of PEDOT (5.1 eV) and
the estimated IP of the P4AQs (∼5.3-5.4 eV) and the
imbalanced charge transport in the P4AQs account for
the poor performance of these polymers as emissive
materials in LEDs. Therefore, poly(N-vinylcarbazole)
(PVK) with an IP of 5.8 eV25 was inserted between
PEDOT and P4HQ (or P4OQ) as a hole injection and
hole transport layer in the LEDs. Yellow electrolumi-
necence with an emission peak at 552 nm, which is
identical to the broad, featureless, PL spectra, was again
observed for both P4HQ and P4OQ in LEDs of the type
ITO/PEDOT/PVK/P4HQ(or P4OQ)/Al. This indicates
that the EL emission from these devices comes from only
the P4AQ layer. The current-voltage and luminance-
voltage curves of these bilayer LEDs with emissive
P4HQ or P4OQ are shown in Figure 8B. The diodes had
a turn-on voltage of 5 V and a luminance of 69-86 cd/
F igu r e 7. Reduction (A) and oxidation (B) cyclic voltammo-
grams of P4AQ (5a -5e) thin films in TBAPF6/acetonitrile.
from PPQ (578 nm),3f and this is likely an indication of
a weaker π-stacking interaction in P4AQs than that in
PPQ. The broad, featureless, PL emission bands with a
large Stokes shift of about 150 nm (0.8-0.9 eV) in these
solid-state PL spectra are clearly due to excimer emis-
sion23 in contrast to the observed single chain emission
of the P4AQs in dilute solution. There was no effect of
the alkyl chain length on the PL emission spectra of the
P4AQs, indicating absence of alkyl chain length effects
on the excited-state electronic structures of the P4AQs.
The fluorescence quantum yields (φf) of P4AQs in
dilute chloroform solution and in the solid state are
listed in Table 2. The PL quantum yield in solution
ranges from 16% for P4DQ to 40% for P4HQ. However,
the relative PL quantum efficiency of the P4AQs in the
solid state was rather low, 2-5% (based on a thin film
of ∼10-3 M 9,10-diphenylanthracene in poly(methyl
methacrylate) as a standard (φf ) 83%)).3f The poor
fluorescence quantum yield in thin films of these
polymers is not surprising in view of their efficient
π-stacking and emission from intermolecular excimers.23
Electr och em ica l P r op er ties. To better understand
the electronic structures of the P4AQs in relation to
charge injection processes in polymer devices, we per-
formed cyclic voltammetry measurements on films of the
P4AQs. The reduction and oxidation cyclic voltammo-
grams of P4AQ thin films are shown in Figure 7. All
the poly(4-alkylquinoline)s have reversible reductions
with onset reduction potentials of -1.83 to -1.77 V vs
SCE.24 The formal reduction potentials were also very

8964 Zhu et al.
Macromolecules, Vol. 36, No. 24, 2003
Ta ble 3. Electr olu m in escen t Device P r op er ties of P oly(4-a lk ylqu in olin e)s
a
b
LED configuration
turn-on voltage (V)
Lmax (cd/m2)
J max (mA/cm2)
Vmaxc (V)
EQEd (%)
P4BQ
P4HQ
P4OQ
P4DQ
12.5
14
15
14
5
5
4
21
12
4
116
84
39
20.0
20.0
20.0
21.0
10
10
7.5
23
0.007
0.005
0.003
0.008
0.6
0.22
0.03
P4TDQ
9
37
PVK/P4HQ
PVK/P4OQ
MEH-PPV
MEH-PPV/P4BQ
MEH-PPV/P4HQ
86
69
66
245
700
246
224
500
248
210
10
5
0.043
0.56
13
3.0 (10 V)
0.51
0.07
MEH-PPV/P4OQ
MEH-PPV/P4DQ
MEH-PPV/P4TDQ
5
9.0
9.5
528
392
312
206
316
439
10.0
21.5
14.0
0.055
a
b
d
Maximum luminance. Maximum current. c Maximum voltage. External quantum efficiency.
The electron transport and hole blocking properties
of all the P4AQs were investigated in layered LEDs of
the type ITO/PEDOT/MEH-PPV/5a -5e/Al, where
MEH-PPV was used as the emissive and hole transport
layer. The EL spectra of these layered LEDs are shown
in Figure 9A along with the EL spectrum of a single-
layer MEH-PPV diode. The EL spectra of bilayer
MEH-PPV/P4AQ diodes, with an EL emission maxi-
mum at 583-594 nm, are nearly identical with that of
the single-layer MEH-PPV diode (579 nm). These EL
spectra clearly show that MEH-PPV acts as the emit-
ting layer, and P4AQ functions as an electron transport
and a hole blocking material in these bilayer devices.
We note that the EL spectra of the ITO/PEDOT/MEH-
PPV/P4BQ (or P4DQ)/Al diodes showed a small blue
shift in emission maximum (∼10 nm) when the applied
bias voltage was increased from 10 to 22 V (not shown).
This could be an indication that a small portion of the
EL emission in these diodes comes from P4BQ or P4DQ
at high bias voltages (over 20 V). No such blue shift was
observed in bilayer devices using the other P4AQs.
The performance of the layered MEH-PPV/P4AQ
LEDs was found to be greatly enhanced by the intro-
duction of P4AQ as the electron transport layer. The
luminance-voltage and current-voltage characteristics
of these MEH-PPV/P4AQ diodes are shown in Figure
9B,C. These LEDs showed bright orange-red EL emis-
sion with a turn-on voltage of 5-10 V and a luminance
of 245-700 cd/m2 at 10-23 V, whereas the single-layer
MEH-PPV diode had a turn-on voltage of 4 V and a
luminance of 66 cd/m2 at 7.5 V (Table 3). The maximum
external quantum efficiency of the layered devices
varied from 0.043% for P4BQ to 3.0% for P4HQ. This
represents a factor of 100 enhancement in EL device
efficiency when using P4HQ as an electron transport
material for MEH-PPV-based LEDs. In the case of
MEH-PPV/P4OQ LEDs, the enhancement in EL ex-
ternal quantum efficiency was 17 times compared to the
single-layer MEH-PPV diodes. Thus, the use of P4AQs
as electron transport materials in MEH-PPV-based
LEDs has resulted in substantial enhancement in the
LED performance. We expect that the poly(4-alkyl-
quinoline)s could also be used as electron transport
materials for other electroluminescent polymers includ-
ing arylene vinylene polymers and polyfluorenes.
F igu r e 8. (A) EL spectra of P4HQ (5b), P4OQ (5c), and
P4TDQ (5e). (B) Current-voltage and luminance-voltage
characteristics of ITO/PEDOT/PVK/5b (or 5c)/Al LEDs.
m2 at 10 V. The external quantum efficiency was 0.6%
for P4HQ and 0.22% for P4OQ. These results suggest
that the device performance (luminance, turn-on volt-
age, and EQE) can be substantially improved by finding
an optimum hole injection and transport layer for P4AQ
LEDs. Although these P4AQ LEDs are not optimized,
the low device performance when they are used as
emissive EL materials is consistent with their low solid-
state PL quantum yields. Because of their large ioniza-
tion potentials, high electron affinities, and poor solid-
state PL quantum yields, the poly(4-alkylquinoline)s are
thus more promising as hole blocking and electron
transport materials that could be used in conjunction
with other more emissive conjugated polymers for the
construction of multilayer or blend LEDs.2,3,9
Con clu sion s
Novel poly(4-alkylquinoline)s with 100% head-to-tail
regioregularity have been synthesized by self-condensa-
tion polymerization of new AB-type monomers. Wide-
angle X-ray diffraction studies showed that solution-

Macromolecules, Vol. 36, No. 24, 2003
Poly(4-alkylquinoline)s 8965
Exp er im en ta l Section
Ma ter ia ls. Valeryl chloride, heptanoyl chloride, nonanoyl
chloride, myristoyl chloride, 4-ethylaniline, zinc chloride,
hydrochloric acid, methylene chloride, acetic anhydride, potas-
sium permanganate, magnesium oxide, nitric acid, ethanol,
diphenyl phosphate (DPP), poly(ethylenedioxythiophene)/poly-
(styrenesulfonic acid) (PEDOT; solution in water), and poly-
(N-vinylcarbazole) (PVK) were used as received from Aldrich.
Poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene)
(MEH-PPV, Mw ∼ 85 000) was purchased from American Dye
Source, Inc. Undecanoyl chloride was used as received from
TCI. m-Cresol was purified by distillation under reduced
pressure.
Mon om er Syn th esis. 1-(5-Acetyl-2-aminophenyl)pentan-
1-one (4a ), 1-(5-acetyl-2-aminophenyl)heptan-1-one (4b), 1-(5-
acetyl-2-aminophenyl)nonan-1-one (4c), 1-(5-acetyl-2-amino-
phenyl)undecan-1-one (4d), and 1-(5-acetyl-2-aminophenyl)tetra-
decan-1-one (4e) were synthesized in four steps by modifying
a reported method,19 as shown in Scheme 1.
1-(2-Am in o-5-eth ylph en yl)pen tan -1-on e (1a). To a stirred
solution of 10.2 g (0.073 mol) of zinc chloride in 24.3 g (0.202
mol) of valeryl chloride maintained at 120 °C, 6.1 g (0.05 mol)
of 4-ethylaniline was added in portions. The resulting mixture
was refluxed at 180 °C for 2 h. After cooling to 135 °C, 80 mL
of 9 M hydrochloric acid was slowly added in portions, and
the mixture was stirred and refluxed at 135 °C for 25 h. After
the mixture was cooled to 35 °C, 80 mL of methylene chloride
was added, followed by about 80 mL of water. The mixture
was extracted with CH2Cl2, and the organic layer was sequen-
tially washed with 3 M aqueous hydrochloric acid solution, 3
M aqueous sodium hydroxide solution, and water. The organic
layer was dried over sodium sulfate, filtered, and evaporated
under vacuum, yielding a dark viscous oil. The crude product
was purified on silica gel column (10% ethyl acetate in hexane
as eluent) to yield 6.4 g of compound 1a (62%) of yellow
needles; mp 58.2-58.9 °C. 1H NMR (500 MHz, CDCl3): δ 7.55
(s, 1H), 7.14 (d, 1H), 6.68 (d, 1H), 2.93 (t, 2H), 2.54 (m, 2H),
1.69 (m, 2H), 1.35 (m, 2H), 1.19 (t, 3H), 0.93 (t, 3H).
N-(4-E t h yl-2-p en t a n oylp h en yl)a cet a m id e (2a ). Acetic
anhydride (5.77 mL, 61.2 mmol) was added to a solution of 1a
(6 g, 29.3 mmol) in 100 mL of benzene, and the solution was
refluxed for 2 h. The solvent was evaporated to yield a light
yellow solid. The obtained solid was dissolved in methylene
chloride, washed with 10% aqueous NaOH solution and water,
and dried over sodium sulfate. The solvent was evaporated to
afford a light yellow solid. The crude product was purified by
flash column chromatography (silica gel, 15% ethyl acetate in
hexane), and compound 2a (6.9 g) was obtained as a white
solid with 95% yield; mp 51.1-52.5 °C. 1H NMR (500 MHz,
CDCl3): δ 8.63 (d, 1H), 7.72 (s, 1H), 7.40 (d, 1H), 3.03 (t, 2H),
2.67 (m, 2H), 2.23 (s, 3H), 1.72 (m, 2H), 1.44 (m, 2H), 1.26 (t,
3H), 0.99 (t, 3H).
N-(4-Acetyl-2-pen tan oylph en yl)acetam ide (3a). A three-
necked flask was charged with 3 g (75 mmol) of magnesium
oxide, 10 mL (217 mmol) of concentrated nitric acid, and 700
mL of water. To the resulting solution, 6.9 g (28 mmol) of 2a
and 11.6 g (73 mmol) of potassium permanganate were added.
The reaction mixture was heated with stirring (magnetic bar)
at 80 °C for 10 h. After cooling to room temperature, the
solution was purged with a stream of gaseous sulfur dioxide
to dissolve the manganese dioxide. The aqueous layer of the
reaction mixture was extracted with methylene chloride,
washed with water, and dried over sodium sulfate. After
evaporating the solvent, the crude product was purified by
flash column chromatography (silica gel, 30% ethyl acetate in
hexane) to afford compound 3a (1.82 g) as colorless needles
with 25% yield; mp 91.0-91.9 °C. 3.2 g of 2a was recovered.
1H NMR (500 MHz, CDCl3): δ 8.85 (d, 1H), 8.60 (s, 1H), 8.07
(d, 1H), 3.11 (t, 2H), 2.63 (s, 3H), 2.25 (s, 3H), 1.74 (m, 2H),
1.42 (m, 2H), 0.98 (t, 3H).
F igu r e 9. (A) EL spectra, (B) luminance-voltage character-
istics, and (C) current-voltage characteristics of ITO/PEDOT/
MEH-PPV/P4AQ(5a -5e)/Al diodes and a single-layer MEH-
PPV diode.
cast films of the regioregular poly(4-alkylquinoline)s
have highly ordered, self-organized, π-stacked lamellar
structures in which the packing of the alkyl side chains
takes an interdigitation mode with a tilting angle of
about 52°. The poly(4-alkylquinoline)s emit blue light
in dilute solutions and exhibit yellow photoluminescence
and electroluminescence in the solid state. Initial use
of the new n-type polymers as electron transport
materials in MEH-PPV-based LEDs has resulted in a
large enhancement in the device performance (a lumi-
nance of up to 700 cd/m2 and an external quantum
efficiency of up to 3.0%), demonstrating that they are
promising electron transport materials for polymer
LEDs.
1-(5-Acetyl-2-a m in op h en yl)p en ta n -1-on e (4a ). To a so-
lution of 3a (1.8 g, 6.9 mmol) in 60 mL of ethanol was added
35 mL (69.2 mmol) of 2 M aqueous NaOH. The reaction
mixture was refluxed for 1 h. After the ethanol was evaporated,

8966 Zhu et al.
Macromolecules, Vol. 36, No. 24, 2003
the aqueous layer was extracted with methylene chloride,
washed with water, and dried over sodium sulfate. The
obtained yellow solid was purified by flash column chroma-
tography (silica gel, 30% ethyl acetate in hexane), followed by
recrystallization from ethanol to afford compound 4a (1.28 g)
as light yellow needles with 85% yield; mp 88.0-88.9 °C. Anal.
Calcd for C13H17NO2: C, 71.21; H, 7.81; N, 6.39. Found: C,
71.30; H, 7.83; N, 6.35. 1H NMR (500 MHz, CDCl3): δ 8.48 (s,
1H), 7.86 (d, 1H), 6.65 (d, 1H), 3.02 (t, 2H), 2.52 (s, 3H), 1.74
(m, 2H), 1.43 (m, 2H), 0.98 (t, 3H). FT-IR (KBr, cm-1): 3427,
3315, 2952, 2872, 1671, 1601, 1488, 1370, 1253, 1170, 962, 824,
664.
and obtained as white needles with 88% yield; mp 46.6-47.4
1
°C. H NMR (500 MHz, CDCl3): δ 8.65 (d, 1H), 7.72 (s, 1H),
7.41 (d, 1H), 3.03 (t, 2H), 2.68 (m, 2H), 2.23 (s, 3H), 1.74 (m,
2H), 1.30 (m, 14H), 1.27 (t, 3H), 0.90 (t, 3H).
N-(4-Acetyl-2-u n d eca n oylp h en yl)a ceta m id e (3d ). Com-
pound 3d was prepared by a procedure similar to that of 3a
and obtained as colorless needles with 24% yield; mp 62.1-
64 °C. 1H NMR (500 MHz, CDCl3): δ 8.87 (d, 1H), 8.62 (s, 1H),
8.11 (d, 1H), 3.13 (t, 2H), 2.64 (s, 3H), 2.29 (s, 3H), 1.75 (m,
2H), 1.30 (m, 17H), 0.90 (t, 3H).
1-(5-Acetyl-2-a m in op h en yl)u n d eca n -1-on e (4d ). This
compound was prepared by a procedure similar to that of 4a
and obtained as light yellow needles with 92% yield; mp 67.9-
68.6 °C. Anal. Calcd for C19H29NO2: C, 75.21; H, 9.63; N, 4.62.
Found: C, 75.26; H, 9.24; N, 4.64. 1H NMR (500 MHz,
CDCl3): δ 8.49 (s, 1H), 7.87 (d, 1H), 6.67 (d, 1H), 3.03 (t, 2H),
2.56 (s, 3H), 1.75 (m, 2H), 1.30 (m, 17H), 0.90 (t, 3H). FT-IR
(KBr, cm-1): 3444, 3332, 2920, 2851, 1657, 1606, 1496, 1376,
1265, 1242, 1183, 978, 828, 668.
1-(2-Am in o-5-eth ylp h en yl)h ep ta n -1-on e (1b). This com-
pound was prepared by a procedure similar to that of 1a , using
heptanoyl chloride instead of valeryl chloride. Compound 1b
1
(10 g) was obtained as a yellow viscous oil with 52% yield. H
NMR (500 MHz, CDCl3): δ 7.56 (s, 1H), 7.14 (d, 1H), 6.62 (d,
1H), 6.15 (s, 2H), 2.95 (t, 2H), 2.58 (m, 2H), 1.74 (m, 2H), 1.35
(m, 6H), 1.22 (t, 3H), 0.92 (t, 3H).
N-(4-Eth yl-2-h eptan oylph en yl)acetam ide (2b). This com-
pound was prepared by a procedure similar to that of 2a and
obtained as a colorless viscous oil with 95% yield. 1H NMR
(500 MHz, CDCl3): δ 8.63 (d, 1H), 7.72 (s, 1H), 7.40 (d, 1H),
3.03 (t, 2H), 2.67 (m, 2H), 2.23 (s, 3H), 1.73 (m, 2H), 1.36 (m,
6 H), 1.26 (t, 3H), 0.92 (t, 3H).
1-(2-Am in o-5-eth ylp h en yl)tetr a d eca n -1-on e (1e). Com-
pound 1e was prepared by a procedure similar to that of 1a
and isolated as a colorless solid with 50% yield; mp 51.9-52.8
1
°C. H NMR (500 MHz, CDCl3): δ 7.58 (s, 1H), 7.16 (d, 1H),
6.70 (d, 1H), 5.58 (broad, 2H), 2.96 (t, 2H), 2.59 (m, 2H), 1.73
(m, 2H), 1.24 (m, 23H), 0.90 (t, 3H).
N-(4-Acetyl-2-h ep ta n oylp h en yl)a ceta m id e (3b). This
compound was prepared by a procedure similar to that of 3a
and was isolated as colorless needles with 25% yield; mp 78.2-
N-(4-Eth yl-2-tetr adecan oylph en yl)acetam ide (2e). Com-
pound 2e was prepared by a procedure similar to that of 2a
and obtained as white needles with 87% yield; mp 49.5-50.8
1
1
78.9 °C. H NMR (500 MHz, CDCl3): δ 8.85 (d, 1H), 8.60 (s,
°C. H NMR (500 MHz, CDCl3): δ 8.65 (d, 1H), 7.71 (s, 1H),
1H), 8.09 (d, 1H), 3.11 (t, 2H), 2.62 (s, 3H), 2.27 (s, 3H), 1.76
(m, 2H), 1.37 (m, 6H), 0.93 (t, 3H).
7.41 (d, 1H), 3.03 (t, 2H), 2.68 (m, 2H), 2.22 (s, 3H), 1.74 (m,
2H), 1.26 (m, 23H), 0.90 (t, 3H).
1-(5-Acet yl-2-a m in op h en yl)h ep t a n -1-on e (4b ). Com-
pound 4b was prepared by a procedure similar to that of 4a
and obtained as light yellow needles with 90% yield; mp 82.1-
82.6 °C. Anal. Calcd for C15H21NO2: C, 72.84; H, 8.56; N, 5.66.
Found: C, 72.76; H, 8.55; N, 5.65. 1H NMR (500 MHz,
CDCl3): δ 8.48 (s, 1H), 7.86 (d, 1H), 6.82 (broad, 2H), 6.65 (d,
1H), 3.02 (t, 2H), 2.53 (s, 3H), 1.74 (m, 2H), 1.35 (m, 6H), 0.91
(t, 3H). FT-IR (KBr, cm-1): 3427, 3314, 2947, 2864, 1663, 1605,
1493, 1364, 1232, 1187, 967, 830, 666.
1-(2-Am in o-5-eth ylp h en yl)n on a n -1-on e (1c). This com-
pound was prepared by a procedure similar to that of 1a and
isolated as a light yellow oil with 56% yield. 1H NMR (500
MHz, CDCl3): δ 7.56 (s, 1H), 7.14 (d, 1H), 6.63 (d, 1H), 6.15
(s, 2H), 2.95 (t, 2H), 2.58 (m, 2H), 1.74 (m, 2H), 1.32 (m, 10H),
1.23 (t, 3H), 0.91 (t, 3H).
N-(4-Acetyl-2-tetr adecan oylph en yl)acetam ide (3e). Com-
pound 3e was prepared by a procedure similar to that of 3a
and obtained as colorless needles with 25% yield; mp 96.6-
1
97.3 °C. H NMR (500 MHz, CDCl3): δ 8.87 (d, 1H), 8.62 (s,
1H), 8.11 (d, 1H), 3.11 (t, 2H), 2.64 (s, 3H), 2.29 (s, 3H), 1.74
(m, 2H), 1.30 (m, 23H), 0.90 (t, 3H).
1-(5-Acetyl-2-a m in op h en yl)tetr a d eca n -1-on e (4e). This
compound was prepared by a procedure similar to that of 4a
and obtained as light yellow needles with 90% yield; mp 83.6-
84.4 °C. Anal. Calcd for C22H35NO2: C, 76.47; H, 10.21; N, 4.05.
Found: C, 76.39; H, 10.24; N, 3.96. 1H NMR (500 MHz,
CDCl3): δ 8.49 (s, 1H), 7.87 (d, 1H), 6.66 (d, 1H), 3.03 (t, 2H),
2.56 (s, 3H), 1.74 (m, 2H), 1.32 (m, 23H), 0.90 (t, 3H). FT-IR
(KBr, cm-1): 3407, 3307, 2920, 2850, 1658, 1611, 1472, 1364,
1227, 1178, 967, 848, 720, 667.
N-(4-Eth yl-2-n on a n oylp h en yl)a ceta m id e (2c). This com-
pound was prepared by a procedure similar to that of 2a and
obtained as white needles with 93% yield; mp 39.3-40.0 °C.
1H NMR (500 MHz, CDCl3): δ 8.65 (d, 1H), 7.72 (s, 1H), 7.41
(d, 1H), 3.03 (t, 2H), 2.68 (m, 2H), 2.22 (s, 3H), 1.74 (m, 2H),
1.30 (m, 10H), 1.27 (t, 3H), 0.91 (t, 3H).
P olym er Syn th esis. The synthesis of the regioregular poly-
(4-alkylquinoline-2,6-diyl)s (5a -5e) is shown in Scheme 1.
P oly(4-bu tylqu in olin e-2,6-d iyl) (P 4BQ, 5a ). 1-(5-Acetyl-
2-aminophenyl)pentan-1-one (4a , 800 mg, 3.65 mmol) was
added to a solution of 1.5 g of diphenyl phosphate (DPP) and
3 g of freshly distilled m-cresol in a cylindrical reaction flask
fitted with a mechanical stirrer, a gas inlet, and two sidearms.
The reactor was purged with argon for 20 min before the
temperature was raised slowly to 70 °C. The reaction was run
at this temperature for 1 h. The temperature was then raised
slowly to 180 °C within 6 h and maintained for 5 days under
static argon. As the viscosity of the reaction mixture increased
with time, additional m-cresol was added to the reaction
mixture to facilitate efficient stirring. Thereafter, the reaction
was quenched by cooling it down to room temperature under
argon and precipitating it in 300 mL of 10% triethylamine/
ethanol solvent mixture. The precipitated polymer was col-
lected by suction filtration and purified by Soxhlet extraction
with 10% triethylamine/ethanol mixture for 48 h. The polymer
was dried under vacuum at 60 °C for 24 h to give a dark red
N-(4-Acetyl-2-n on an oylph en yl)acetam ide (3c). This com-
pound was prepared by a procedure similar to that of 3a and
obtained as colorless needles with 27% yield; mp 79.5-80.2
1
°C. H NMR (500 MHz, CDCl3): δ 8.87 (d, 1H), 8.62 (s, 1H),
8.11 (d, 1H), 3.13 (t, 2H), 2.64 (s, 3H), 2.30 (s, 3H), 1.78 (m,
2H), 1.32 (m, 10H), 0.89 (t, 3H).
1-(5-Acetyl-2-am in oph en yl)n on an -1-on e (4c). Compound
4c was prepared by a procedure similar to that of 4a and
obtained as light yellow needles with 92% yield; mp 72.4-73.2
°C. Anal. Calcd for C17H25NO2: C, 74.14; H, 9.15; N, 5.09.
Found: C, 74.04; H, 9.02; N, 5.06. 1H NMR (500 MHz,
CDCl3): δ 8.50 (s, 1H), 7.87 (d, 1H), 6.81 (broad, 2H), 6.68 (d,
1H), 3.03 (t, 2H), 2.56 (s, 3H), 1.74 (m, 2H), 1.30 (m, 10H),
0.91 (t, 3H). FT-IR (KBr, cm-1): 3445, 3332, 2920, 2865, 1656,
1607, 1495, 1375, 1254, 1182, 977, 830, 667.
1
solid (582 mg, 87%). H NMR (300 MHz, CF3COOD): δ 9.38
1-(2-Am in o-5-eth ylp h en yl)u n d eca n -1-on e (1d ). Com-
pound 1d was prepared by a procedure similar to that of 1a
and isolated as a light yellow solid with 45% yield; mp 40.8-
(s, 1H), 8.92 (s, 2H), 8.60 (s, 1H), 3.78 (s, 2H), 3.11 (s, terminal
acetyl protons), 2.12 (s, 2H), 1.76 (s, 2H), 1.19 (s, 3H). FT-IR
(film, cm-1): 2955, 2929, 2870, 1593, 1557, 1468, 1427, 1341,
1244, 881, 843.
1
42.2 °C. H NMR (500 MHz, CDCl3): δ 7.56 (s, 1H), 7.14 (d,
1H), 6.63 (d, 1H), 6.14(broad, 2H), 2.95 (t, 2H), 2.58 (m, 2H),
1.74 (m, 2H), 1.30 (m, 14H), 1.23 (t, 3H), 0.90 (t, 3H).
N-(4-Eth yl-2-u n d eca n oylp h en yl)a ceta m id e (2d ). Com-
pound 2d was prepared by a procedure similar to that of 2a
P oly(4-h exylqu in olin e-2,6-d iyl) (P 4HQ, 5b). This poly-
mer was prepared by a procedure similar to that of 5a and
isolated as an orange solid with 91% yield. 1H NMR (300 MHz,
CF3COOD): δ 9.39 (s, 1H), 8.92 (s, 2H), 8.60 (s, 1H), 3.77

Macromolecules, Vol. 36, No. 24, 2003
Poly(4-alkylquinoline)s 8967
(broad, 2H), 3.11 (s, terminal acetyl protons), 2.16 (broad, 2H),
1.50 (broad, 6H), 1.01 (s, 3H). FT-IR (film, cm-1): 2927, 2857,
1593, 1558, 1508, 1466, 1340, 1234, 881, 842.
ITO-coated glass substrate. Electroluminescence (EL) spectra
were measured on a PTI QuantaMaster model C-60/2000
spectrofluorometer (Photon Technology International Inc.). The
electrical characteristics of the devices were measured on an
HP4155A semiconductor parameter analyzer together with a
Grasby S370 optometer equipped with a calibrated luminance
sensor head. The EL quantum efficiencies of the diodes were
determined by using procedures similar to those previously
reported.3f More details of our device fabrication and charac-
terization can be found in our previous reports.3c-h,9 All the
fabrications and measurements were done under ambient
laboratory conditions.
P oly(4-octylqu in olin e-2,6-d iyl) (P 4OQ, 5c). This polymer
was prepared by a procedure similar to that of 5a and obtained
1
as an orange solid with 87% yield. H NMR (300 MHz, CF3-
COOD): δ 9.37 (s, 1H), 8.91 (s, 2H), 8.59 (s, 1H), 3.76 (broad,
2H), 3.09 (s, terminal acetyl protons), 2.14 (broad, 2H), 1.39
(broad, 10H), 0.94 (s, 3H). FT-IR (film, cm-1): 2925, 2854,
1593, 1558, 1510, 1467, 1340, 1234, 880, 842.
P oly(4-d ecylqu in olin e-2,6-d iyl) (P 4DQ, 5d ). P4DQ was
prepared by a procedure similar to that of 5a and isolated as
a yellow solid with 90% yield. 1H NMR (300 MHz, CF3-
COOD): δ 9.28 (s, 1H), 8.79 (s, 2H), 8.51 (s, 1H), 3.74 (broad,
2H), 3.05 (s, terminal acetyl protons), 2.07 (broad, 2H), 1.31
(broad, 14H), 0.85 (s, 3H). FT-IR (film, cm-1): 2924, 2853,
1593, 1557, 1511, 1469, 1342, 1233, 881, 842.
P oly(4-tr id ecylqu in olin e-2,6-d iyl) (P 4TDQ, 5e). This
polymer was prepared by a procedure similar to that of 5a
and isolated as a yellow solid with 90% yield. 1H NMR (300
MHz, CF3COOD): δ 9.38 (s, 1H), 8.91 (s, 2H), 8.61 (s, 1H),
3.78 (broad, 2H), 3.10 (s, terminal acetyl protons), 2.17 (broad,
2H), 1.39 (broad, 20H), 0.94 (s, 3H). FT-IR (film, cm-1): 2929,
2858, 1596, 1564, 1468, 1340, 1300, 1237, 885, 845.
Ack n ow led gm en t. This work was supported by the
Army Research Office TOPS MURI (DAAD19-01-1-
0676), the Air Force Office of Scientific Research (F49620-
03-1-0162), and in part by the Office of Naval Research.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra,
FT-IR spectra, and TGA thermograms of the poly(4-alkyl-
quinoline)s (P4AQs). This material is available free of charge
via the Internet at http://pubs.acs.org.
Refer en ces a n d Notes
Ch a r a cter iza tion . FT-IR spectra were taken on a Perkin-
Elmer 1720 FTIR spectrophotometer with KBr pellets or NaCl
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determined by using a perylene standard (10-6 M in chloro-
form, Φf ) 87%).26 Approximate relative fluorescence quantum
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a thin film of ∼10-3 M 9,10-diphenylanthracene in poly(methyl
methacrylate) as a standard (φf ) 83%).3f Cyclic voltammetry
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Research potentiostat/galvanostat instrument (model 273A) in
an electrolyte solution of 0.1 M tetrabutylammonium hexafluo-
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